Remove the last hardcoding from PhabricatorMetaMTAReceivedMail

Summary:
Moves all remaining mail handling into ReplyHandlers.

Farewell, getPhabricatorToInformation()! You were a bad method and no one liked you.

Ref T1205.

Test Plan:

• Used test console to send mail to Revisions, Tasks, Conpherences and Commits (these all actually work).
• Used test console to send mail to Requests, Macros, Questions and Mocks (these accept the mail but don't do anything with it, but didn't do anything before either).

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1205

Differential Revision: https://secure.phabricator.com/D5953